It's not even that he isn't girly enough, it's that he isn't cool enough. All femboys are inherently cool.
Though it would be nice to have a femboy character who doesn't act like an "ideal" woman from before the 20th century. (Who doesn't present themselves, begging to get buttfucked as soon as you meet them)
You can, I'm pretty sure Savin has mentioned it somewhere.
Also what's with everyone wanting to fuck family members? You guys know there's like, a literal universe of sexy aliens you guys can bone who aren't related to you?
Then again, Shade being half alien she might be so genetically diverse from you that she might not even be considered a family member in terms of genetics.
Also if TiTS is an infinite universe, there full well may be a race of aliens so genetically similar to you that they could be considered your siblings.
Hmm...
Twincest planet when?
Incest is muh fetish
But seriously, there's several reasons people like it. The taboo/forbidden fruit factor is a huge part of it. There's also the idea that if you're close to your sibling, sex with them will be more satisfying since they know you well enough to be VERY effective at pleasuring you, though that doesn't really apply to Shade or Jill. Finally, for me, there's a big thrill both sexually and emotionally in the idea of taking a good relationship with your family member to the 'next level', achieving the ultimate connection with someone you love.
Parental incest is another matter altogether. For me at least, there's a very uncomfortable and unhealthy power dynamic issue there; your parents have formed the foundation of your world for literally your entire life and it's very easy to abuse that power (and not just in a sexual way, either).
Maybe it's because I'm closer to my dad than to my mom but I'm more open to mother/child incest than father/child; the latter feels to me like a perversion and betrayal of the loving relationship I have with my father. Brother/brother incest similarly squicks me out, because I have two younger brothers who I love to death, whereas I have no sisters, making bro/sis or sis/sis less emotionally triggering to me. (Or it could just be residual heteronormativity rising up in me, Iunno. I hope not.)
That's just my personal baggage, though, I'm not here to kinkshame.